It is desirable in many applications to provide a structure, such as a radome structure, which will permit the transmission of energy in either direction therethrough only over a selected frequency range, or pass band of frequencies, and effectively to reject the transmission of energy at frequencies outside the pass band. In this way the radome structure will prevent the transmission of external signals through the structure to the equipment housed therein a frequencies outside the sometimes relatively narrow pass band of operation of such equipment so that the radome structure acts as an effective shield to such externally impinging electromagnetic energy.